Method of network entry in OFDM multi-carrier wireless communications systems

ABSTRACT

A unified two-stage network entry procedure is provided for OFDM multi-carrier wireless communications systems. During a first stage, a mobile station performs a common network entry procedure using a primary radio frequency carrier and then exchanges multi-carrier capability information with a base station. In one embodiment, the base station transmits a network entry allowance indicator to assist the mobile station in selecting the primary carrier. The network entry allowance indicator comprises information of preference of one or more available carriers. During a second stage, the mobile station enables multi-carrier transmission over multiple frequency channels if both the mobile station and the base station support multi-carrier capability. Before enabling multi-carrier transmission, the mobile station may optionally perform additional ranging by transmitting a ranging request for a secondary carrier. In one embodiment, the base station replies with a ranging response in response to the ranging request through the primary carrier.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation, and claims priority under 35 U.S.C.§120 from nonprovisional U.S. patent application Ser. No. 12/387,633,entitled “Method of Network Entry in OFDM Multi-Carrier WirelessCommunications Systems,” filed on May 4, 2009, the subject matter ofwhich is incorporated herein by reference. Application Ser. No.12/387,633, in turn, claims priority under 35 U.S.C. §119 from U.S.Provisional Application No. 61/050,277, entitled “Control Structure,Ranging and Initialization Procedure for Multi-band OFDMA Systems,”filed on May 5, 2008; U.S. Provisional Application No. 61/156,574,entitled “Methods for Configuring Multi-Carrier Transmission in OFDMMulti-Carrier Systems,” filed on Mar. 2, 2009; U.S. ProvisionalApplication No. 61/154,022, entitled “Method of Network Entry in OFDMAMulti-Carrier Systems,” filed on Feb. 20, 2009, the subject matter ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless networkcommunications, and, more particularly, to network entry in OFDMmulti-carrier systems.

BACKGROUND

In current wireless communications systems, 5 MHz˜10 MHz radiobandwidths are typically used for up to 100 Mbps peak transmission rate.Much higher peak transmission rate is required for next generationwireless systems. For example, 1 Gbps peak transmission rate is requiredby ITU-R for IMT-Advanced systems such as the 4^(th) generation (“4G”)mobile communications systems. The current transmission technologies,however, are very difficult to perform 100 bps/Hz transmission spectrumefficiency. In the foreseeable next few years, only up to 15 bps/Hztransmission spectrum efficiency can be anticipated. Therefore, muchwider radio bandwidths (i.e., at least 40 MHz) will be necessary fornext generation wireless communications systems to achieve 1 Gbps peaktransmission rate.

Orthogonal Frequency Division Multiplexing (OFDM) is an efficientmultiplexing protocol to perform high transmission rate over frequencyselective channel without the disturbance from inter-carrierinterference. OFDM has been adopted by both IEEE 802.16m and LTE draftstandards and is anticipated to be a foundation of next generationwireless communications systems. Based on OFDM, various multiple accessschemes such as OFDMA, OFDM/CDMA, and OFDM/TDMA have been developed andutilized in multi-user wireless systems.

FIG. 1 (Prior Art) illustrates two typical architectures to utilize muchwider radio bandwidth for OFDM systems. In a traditional OFDM system, asingle radio frequency (RF) carrier is used to carry one wideband radiosignal, and in an OFDM multi-carrier system, multiple RF carriers areused to carry multiple narrower band radio signals. In the example ofFIG. 1, a traditional OFDM system 1 uses a single RF carrier #1 to carrya wideband radio signal #1, transmitted through one frequency channel #1(i.e., 40 MHz Bandwidth, 4096 FFT). On the other hand, an OFDMmulti-carrier system 11 uses four RF carriers #1-#4 to carry fournarrower band radio signals #1-#4, each transmitted through acorresponding 10 MHz frequency channel #1-#4 (i.e., 10 MHz Bandwidth,1024 FFT).

An OFDM multi-carrier system has various advantages as compared to atraditional OFDM system. First, an OFDM multi-carrier system has lowerPeak to Average Power Ratio (PAPR) for uplink transmission because ofsmaller FFT size for each carrier. Second, it is easier to supportbackward compatibility with legacy OFDM systems. For example, thefrequency channels in an OFDM multi-carrier system are partitioned into10 MHz bandwidth to fit legacy WiMAX systems. Third, current hardwaredesign such as legacy PHY layer design can be better reused by the samefrequency channel bandwidths and parameters. Finally, in an OFDMmulti-carrier system, it is possible to have more flexibility in MobileStations (MSs) that support different number of carriers and performdifferent level of service capabilities. Because of such advantages,OFDM multi-carrier systems have become the baseline system architecturein IEEE 802.16m and LTE-Advanced draft standards to fulfill IMT-Advancedsystem requirements. It is thus desirable to provide a unified networkentry procedure to enable the operation of OFDM multi-carrier systems.

SUMMARY

A unified two-stage network entry procedure is provided for a mobilestation and a base station in an OFDM multi-carrier wirelesscommunications system. During a first stage of common network entryprocedure, the mobile station selects one of the available radiofrequency carriers as the primary carrier to perform network entry andranging. The mobile station also exchanges multi-carrier capabilityinformation with the base station. During a second stage of additionalnetwork entry procedure, the mobile station enables multi-carriertransmission over multiple frequency channels if both the mobile stationand the base station support multi-carrier capability. Before enablingmulti-carrier transmission, the mobile station may optionally performadditional ranging by transmitting a ranging request for a secondarycarrier. In response to the ranging request, the base station may replywith a ranging response through the primary carrier.

In one novel aspect, the base station transmits a network entryallowance indicator to assist the mobile station in selecting theprimary carrier. The network entry allowance indicator comprisesinformation of preference of one or more available carriers. In oneembodiment, such preference may be based on load balancing condition. Byreceiving such information from the base station, the mobile station isable to select a carrier as its primary carrier and achieve load balanceduring the initial stage of network entry procedure. In anotherembodiment, such preference may be based on other network parameters toserve other purposes such as avoiding sub-carrier misalignmentoperation.

In another novel aspect, the unified two-stage network entry procedureis compatible between both multi-carrier and single-carrier basestations and mobile stations in an OFDM wireless system. Based on themulti-carrier capability information exchanged during the common networkentry procedure, the mobile station can determine whether to proceed tothe second stage of additional network entry procedure. If either themobile station or the base station supports single-carrier capability,then network entry is performed only for the primary carrier and noadditional network entry is necessary. On the other hand, if both themobile station and the base station support multi-carrier capability,then the mobile station may enable multi-carrier transmission afterreconfiguring its hardware and performing additional ranging for thesecondary carrier.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (Prior Art) illustrates two typical architectures to utilize muchwider radio bandwidth for OFDM systems.

FIG. 2 illustrates a network entry procedure of an OFDM wireless networkin accordance with one novel aspect.

FIG. 3 is a flow chart of a method of network entry procedure for OFDMmulti-carrier systems in accordance with one novel aspect.

FIG. 4 is a simplified block diagram of a multi-carrier base station.

FIG. 5 is a simplified block diagram of a multi-carrier mobile station.

FIG. 6 illustrates an example of common network entry procedure withoutnetwork entry allowance indicator.

FIG. 7 illustrates an example of common network entry procedure withnetwork entry allowance indicator.

FIG. 8 illustrates an example of selecting a primary RF carrier forcommon network entry procedure to avoid sub-carrier misalignmentoperation.

FIG. 9 illustrates network entry compatibility among single-carrierand/or multi-carrier base stations and mobile stations.

FIG. 10 illustrates an example of performing additional network entryand enabling multi-carrier transmission in an OFDM wireless system.

FIG. 11 illustrates the activation of a secondary carrier to supportdata transmission over multiple carriers simultaneously in an OFDMwireless system.

FIG. 12 is a diagram of additional network entry with ranging procedurebefore activating a secondary RF carrier for data transmission in anOFDM wireless system.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 illustrates a network entry procedure of an OFDM wireless network20 in accordance with one novel aspect. OFDM wireless network 20 is amulti-carrier communications system that comprises a multi-carrier basestation BS22 and a multi-carrier mobile station MS24. Both BS22 and MS24support four radio frequency (RF) carriers #1-#4. In order to access thewireless network, MS24 needs to perform network entry procedure withBS22 to synchronize the time and frequency with BS22 and to negotiateother network capabilities and parameters. As illustrated in FIG. 2, thenetwork entry procedure is divided into two stages: a first stage ofcommon network entry procedure and a second stage of additional networkentry procedure. During the common network entry procedure, MS24 firstselect one of the RF carriers (for example, RF carrier #2, asillustrated in FIG. 2) as the primary RF carrier to perform networkentry. MS24 also exchanges its multi-carrier capability with BS 22during the common network entry procedure. During the additional networkentry procedure, MS24 may optionally perform additional rangingprocedure over a secondary RF carrier (for example, RF carrier #3, asillustrated in FIG. 2). After the ranging procedure is successfullycompleted, MS24 then enables multi-carrier transmission such that datatransmission is supported over both RF carrier #2 and RF carrier #3simultaneously.

FIG. 3 is a flow chart illustrating a method of network entry procedurein OFDM multi-carrier wireless network 20 in more detail. MS24 startswith the first stage of a common network entry procedure that can beused for either a single-carrier or a multi-carrier mobile station. Instep 30, MS24 scans all downlink carriers that might be available toperform network entry. MS24 then establishes synchronization with adownlink carrier in step 31. In step 32, MS24 receives information fromBS22 about whether the synchronized downlink carrier is allowed toperform network entry. If the answer is no, then MS24 goes back to step31 and continues with the next available carrier. If the answer is yes,then MS24 selects that carrier as its primary carrier and proceeds tostep 33 to obtain uplink parameters of the primary carrier. In step 34,MS24 performs ranging for the primary carrier. During the common networkentry procedure, MS24 also exchanges basic capabilities andmulti-carrier capabilities with BS22 in step 35. The informationexchanged in step 35 comprises information such as whether BS22 and MS24support single-carrier and/or multi-carrier capability, the number ofantennas, and/or the number of RF carriers supported by BS22 and MS24.

After ranging is successfully completed in the common network entryprocedure, MS24 then establishes provisioned connection with BS22 overthe primary carrier in step 36. Next, MS24 enters the second stage ofadditional network entry procedure. MS24 first decides whether to enablemulti-carrier transmission in step 37 after multi-carrier capabilitieshave been exchanged with BS22. If the answer is no (for example, BS22does not support multi-carrier capability), then MS24 proceeds to step40 and starts with operation and data transmission over the primarycarrier. If the answer is yes, then MS24 receives parameters of asecondary carrier from BS22 in step 38. In step 39, MS24 performsranging for the secondary carrier. After ranging is successfullycompleted in the secondary carrier, MS24 then enables multi-carriertransmission in step 40 and is able to transmit data over both theprimary carrier and the secondary carrier simultaneously.

FIG. 4 is a simplified block diagram of a multi-carrier base stationBS22. BS22 comprises a common media access control (MAC) module 42, anadaptive multi-carrier controller 44, a plurality of physical layermodules (PHY1-PHY4 as depicted), a plurality of RF transceivers (RF1-RF4as depicted), a plurality of antennas, and a multiplexer 46 thatinterconnects the PHY modules and the RF transceivers. Each PHY module,RF transceiver and antenna forms a transmission module as depicted inFIG. 4. Each transmission module corresponds to the operation of one RFcarrier. Common MAC module 42 is coupled to both adaptive multi-carriercontroller 44 and the transmission modules. By using a common MACmodule, the MAC layer design remains transparent to the underlying RFcarriers and antennas. This unified transceiver architecture for amulti-carrier base station is particularly suitable for the unifiednetwork entry procedure illustrated above with respect to FIG. 2 andFIG. 3.

FIG. 5 is a simplified block diagram of a multi-carrier mobile stationMS24. Similar to BS22 in FIG. 4, MS24 comprises a common MAC module 52,an adaptive multi-carrier controller 54, a plurality of physical layermodules (PHY1-PHY4 as depicted), a plurality of RF transceivers (RF1-RF4as depicted), a plurality of antennas, and a multiplexer 56 thatinterconnects the PHY modules and the RF transceivers. Again, by using acommon MAC module, the MAC layer design of MS24 remains transparent tothe underlying RF carriers and antennas. This unified transceiverarchitecture for a multi-carrier mobile station is particularly suitablefor the unified network entry procedure in accordance with the presentinvention.

In one novel aspect, during the common network entry procedure, a basestation may transmit a network entry allowance indicator to a mobilestation in assisting the mobile station to make preferred primarycarrier selection. FIG. 6 illustrates one embodiment for primary RFcarrier selection during the common network entry procedure. Asillustrated in FIG. 6, five mobile stations MS1-MS5 are in the processof scanning available RF carriers and then selecting one of the RFcarriers as its primary RF carrier to perform network entry with BS62.BS62 provides four carriers #1-#4 available for the mobile stations toperform network entry, but BS62 does not provide additional informationon which of the carriers is either a preferred or a non-preferredcarrier. As a result, each mobile station randomly selects one of thecarriers as its primary carrier. In the example of FIG. 6, MS1 selectscarrier #4, MS2 selects carrier #2, MS3 and MS4 each selects carrier #3,and MS5 selects carrier #1 as the primary carrier, respectively. If suchrandom selection of primary carrier results in load unbalance, then BS62has to use intra-cell handover procedure to switch the primary carriersof the mobile stations.

FIG. 7 illustrates another embodiment for primary RF carrier selectionduring the common network entry procedure. In the example of FIG. 7,base station BS62 transmits a network entry allowance indicator 72 tothe mobile stations MS1-MS5. Network entry allowance indicator 72comprises information such as whether a particular carrier is preferredto be used as the primary carrier. Such preference may be based on loadbalancing and other network parameters. In the example of FIG. 7,carrier #1 has the lightest load and is preferred to be used as theprimary carrier. By receiving such information from BS62 via networkentry allowance indicator 72, mobile stations MS1-MS5 are able to selectRF carrier #1 as its primary carrier and achieve load balance during theinitial stage of network entry procedure. In addition to the initialnetwork entry, the proposed allowance indicator can also be used inhandover reentry procedures.

FIG. 8 illustrates an example of selecting a primary RF carrier duringcommon network entry procedure to avoid sub-carrier misalignmentoperation. In addition to achieving load balance, a network entryallowance indicator may serve other purposes in assisting the selectionfor primary carrier. In an OFDM system, sometimes the center frequencyof a radio signal transmitted over each frequency channel is not thesame as the ones defined in the OFDM system. As illustrated in FIG. 8,multi-carrier base station BS82 supports two RF carriers: carrier #1 andcarrier #1. Carrier #1 carries radio signal #1 and is transmitted byfrequency channel #1. Carrier #2 carries radio signal #2 and istransmitted by frequency channel #2. The center frequency of radiosignal #1 aligns with the predefine center frequency of frequencychannel #1, while the center frequency of radio signal #2 is shiftedfrom the center frequency of frequency channel #2. As a result,multi-carrier mobile station MS84 may not be able to connect with BS82through frequency channel #2 due to unknown center frequency at initialstage. In the example of FIG. 8, BS82 transmits a network entryallowance indicator 86 to MS84, guiding MS84 to select carrier #1 as theprimary carrier. Thus, MS84 will not waste additional time to scan therest carriers with which it would have difficulty to establishconnection.

In another novel aspect, during the common network entry procedure,mobile stations and base stations also exchange multi-carriercapabilities such that the unified two-stage network entry procedure iscompatible with both single-carrier and multi-carrier base stations andmobile stations. FIG. 9 illustrates network entry compatibility amongsingle-carrier and multi-carrier base stations and mobile stations in anOFDM wireless system 90. OFDM wireless system 90 comprises a mixed ofsingle-carrier and multi-carrier base stations and mobile stations, forexample, a single-carrier base station BS92, a multi-carrier basestation BS96, a single-carrier mobile station MS94, and a multi-carriermobile station MS98. In a first scenario, multi-carrier MS94 performsnetwork entry with single-carrier BS92, which only supports RF carrier#1. Under the novel two-stage network entry procedure, MS94 firstselects carrier #1 as the primary carrier and performs ranging duringthe first stage of common network entry. Because BS92 does not supportmulti-carrier capability, the second stage of additional network entryis no longer needed. In a second scenario, single-carrier MS98 performsnetwork entry with multi-carrier BS96. MS98 only supports RF carrier #1while BS96 supports four RF carriers #1-#4. Under the novel two-stagenetwork entry procedure, MS98 selects carrier #1 as the primary carrierand performs ranging during the first stage of common network entry.Because MS98 does not support multi-carrier capability, the second-stageof additional network entry is no longer needed. Thus, the unifiedtwo-stage network entry procedure is compatible for both multi-carrierand single-carrier base stations and mobile stations in OFDM wirelesssystem 90.

If both base stations and mobile stations support multi-carriercapabilities, then the second stage of additional network entryprocedure can be performed after the selection of primary carrier andthe exchange of multi-carrier capabilities. FIG. 10 and FIG. 11illustrate an example of performing additional network entry andenabling multi-carrier transmission in an OFDM wireless system 100. OFDMwireless system 100 comprises a multi-carrier base station BS102 and amulti-carrier mobile station MS104. BS102 supports transmitting radiosignals over four 10 MHz carriers #1-#4 designated by system operator,and MS104 supports transmission over 2×10 MHz carriers utilizing 2048FFT. As illustrated in FIG. 10, MS104 selects carrier #1 as the primarycarrier and turns on the center 1024 FFT to support 10 MHz carrier #1for initial network entry. MS104 only transmits 10 MHz waveform radiosignal by nulling the FFT out of the center 1024 points. MS104 controlsits frequency synthesizer for adjusting the center frequency forscanning the downlink signals transmitted from BS102. As a result, thecenter frequency of MS104 is the same as carrier #1.

FIG. 11 illustrates the activation of a secondary carrier to supportdata transmission over multiple carriers simultaneously in OFDM wirelesssystem 100. In the example of FIG. 11, MS104 activates carrier #2 as itssecondary carrier for multi-carrier transmission. When activating thesecondary carrier, MS104 has to shift its center frequency location toensure its 2048 FFT can cover the bandwidth of both carrier #1 andcarrier #2. Thus, MS104 will need some time to reconfigure its RFfrequency synthesizer and baseband hardware. In addition, MS104 willneed to enable the software control entity for processing the signalingover the secondary carrier. As a result, it is desirable to reserve ashort time period for MS104 to reconfigure and then perform rangingbefore enabling multi-carrier transmission.

FIG. 12 is a diagram of additional network entry with ranging procedurebefore activating a secondary RF carrier for data transmission in anOFDM wireless system. In the example of FIG. 12, a primary carrier isused to carry radio signals through frequency channel #1, and asecondary carrier is used to carry radio signals through frequencychannel #2. After the primary carrier has been selected for initialranging and connected for data transmission, the mobile station performsadditional ranging procedure for the secondary carrier. The mobilestation transmits ranging requests 122 and 124 using ranging channel 126and 128, respectively. Typically, the base station may reply a rangingresponse through the secondary carrier. As illustrated in FIG. 12,however, the base station may reply ranging response 130 through theexisting connection in the primary carrier. Therefore, communicationthrough the primary carrier will not be disrupted when the mobilestation performs ranging through the secondary carrier.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method, comprising: (a) performing a commonnetwork entry procedure using a primary radio frequency (RF) carrier bya mobile station in an OFDM wireless network, wherein the mobile stationobtains uplink parameters of the primary carrier and performs rangingfor the primary carrier; (b) exchanging multi-carrier capabilityinformation with a base station, wherein the multi-carrier capabilityinformation comprises information on number of carriers that can besimultaneously supported by the mobile station and the base station; and(c) enabling multi-carrier transmission over multiple frequency channelsif both the mobile station and the base station support multi-carriercapability.
 2. The method of claim 1, further comprising: (d) obtainingthe primary RF carrier to perform the common network entry procedurebased on a network entry allowance indicator received from the basestation.
 3. The method of claim 2, wherein the obtaining in (d) involvesscanning a plurality of carriers and selecting one of the carriers asthe primary RF carrier to perform the common network entry procedurebased on the network entry allowance indicator.
 4. The method of claim3, wherein the network entry allowance indicator comprises informationof preference of one or more available carriers.
 5. The method of claim3, wherein the network entry allowance indicator comprises informationof loading of one or more available carriers.
 6. The method of claim 1,wherein the common network entry procedure comprises operations tosupport either an initial network entry or a handover network reentry.7. The method of claim 1, further comprising: (d) performing rangingusing a secondary carrier before enabling multi-carrier transmission;and (e) receiving a ranging response for the secondary carrier.
 8. Themethod of claim 7, wherein the secondary carrier is the carrier that themobile station did not perform network entry operation with the basestation.
 9. The method of claim 7, wherein a ranging response for thesecondary carrier is replied through the primary carrier.
 10. The methodof claim 1, wherein a secondary carrier is enabled for multi-carriertransmission, and wherein the enabling in (c) involves shifting centerfrequency and reconfiguring hardware of the mobile station.
 11. Awireless device, comprising: a first transmission module that isoperable in a first radio frequency (RF) carrier by a first frequencychannel; a second transmission module that is operable in a second RFcarrier by a second frequency channel; and an adaptive multi-carriercontroller that selects the first RF carrier to perform a common networkentry procedure with a base station in an OFDM wireless network, whereinthe wireless device exchanges multi-carrier capability with the basestation and thereafter enables the second RF carrier for datatransmission over the second frequency channel if the base stationsupports multi-carrier capability, and wherein the multi-carriercapability comprises information on number of carriers that can besimultaneously supported by the wireless device and the base station.12. The wireless device of claim 11, wherein the adaptive multi-carriercontroller selects the first carrier based on a network entry allowanceindicator provided by the base station.
 13. The wireless device of claim11, wherein the wireless device performs a second ranging for thesecondary carrier before enabling the second carrier for datatransmission.
 14. The wireless device of claim 13, wherein the wirelessdevice receives a ranging response for the secondary carrier through thefirst frequency channel.
 15. The wireless device of claim 11, whereinthe secondary carrier is adjacent to the first carrier, and wherein acenter frequency for data transmission is shifted before enabling thesecond carrier.
 16. The wireless device of claim 11, further comprising:a common MAC layer that is coupled to both the first and the secondtransmission modules, wherein the common MAC layer is also coupled tothe adaptive multi-carrier controller.
 17. A method, comprising: (a)receiving a network entry request by a base station for a primary radiofrequency (RF) carrier from a mobile station in an OFDM wirelessnetwork; (b) exchanging multi-carrier capability information with themobile station, wherein the multi-carrier capability informationcomprises information on number of carriers can be simultaneouslysupported by the mobile station and the base station; and (c) receivingdata signals over multiple frequency channels if both the mobile stationand the base station support multi-carrier capability.
 18. The method ofclaim 17, further comprising: (d) providing a network entry allowanceindicator to the mobile station, wherein the network entry allowanceindicator comprises information of preference of one or more radiofrequency carriers.
 19. The method of claim 17, further comprising: (d)receiving a second network entry request for a secondary carrier beforereceiving data signals over the second carrier; and (e) transmitting aranging response for the secondary carrier.
 20. The method of claim 19,wherein a ranging response for the secondary carrier is replied throughthe primary carrier.